An LED consists of a semi-conductor junction, which emits light due to a current flowing through the junction. At first sight, it would seem that LEDs should make an excellent replacement for the traditional tungsten filament incandescent bulb. At equal power, they give far more light output than do incandescent bulbs, or, what is the same thing, they use much less power for equal light; and their operational life is orders of magnitude larger, namely, 10-100 thousand hours vs. 1-2 thousand hours.
However, LEDs, and bulbs constructed from them, suffer from problems with color. “White” LEDs, which are typically used in bulbs, are today made from one of two processes. In the more common process, a blue-emitting LED is covered with a plastic cap, which, along with other possible optical properties, is coated with a phosphor that absorbs blue light and re-emits light at other wavelengths. A major research effort on the part of LED manufacturers is design of better phosphors, as phosphors presently known give rather poor color rendition. Additionally, these phosphors will saturate if over-driven with too much light, letting blue through and giving the characteristic blue color of over-driven white LEDs.
An additional problem with the phosphor process is that quantum efficiency of absorption and re-emission is less than unity, so that some of the light output of the LED is lost as heat, reducing the luminous efficacy of the LED, and increasing its thermal dissipation problems.
The other process for making a “white” LED today is the use of three (or more) LEDs, typically red, blue and green (RGB), which are placed in close enough proximity to each other to approximate a single source of any desired color. The problem with this process is that the different colors of LEDs age at different rates, so that the actual color produced varies with age. One additional method for getting a “white LED” is to use a colored cover over a blue or other colored LED, such as that made by JKL Lamps™. However, this involves significant loss of light.
LED bulbs have the same problems as do the LEDs they use, and further suffer from problems with the fact the LEDs are point sources. Attempts to do color adjustment by the bulb results in further light intensity loss.
Furthermore, an LED bulb ought to have its light output diffused, so that it has light coming out approximately uniformly over its surface, as does an incandescent bulb, to some level of approximation. In the past, LEDs have had diffusers added to their shells or bodies to spread out the light from the LED. Another method has been to roughen the surface of the LED package. Neither of these methods accomplishes uniform light distribution for an LED bulb, and may lower luminous efficiency. Methods of accomplishing approximate angular uniformity may also involve partially absorptive processes, further lowering luminous efficacy. Additionally, RGB (red, green, blue) systems may have trouble mixing their light together adequately at all angles.
This invention has the object of developing a means to create light from LEDs and LED bulbs that are closer to incandescent color than is presently available, with little or no loss in light intensity.